/*
 *  Copyright 2008-2010 NVIDIA Corporation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */


/*! \file reduce.h
 *  \brief Host implementation reduce.
 */

#pragma once

namespace thrust {

namespace detail {

namespace host {


template < typename InputIterator,
         typename OutputType,
         typename BinaryFunction >
OutputType reduce(InputIterator begin,
                  InputIterator end,
                  OutputType init,
                  BinaryFunction binary_op) {
    // initialize the result
    OutputType result = init;

    while (begin != end) {
        result = binary_op(result, *begin);
        begin++;
    } // end while

    return result;
}

template < typename InputIterator1,
         typename InputIterator2,
         typename OutputIterator1,
         typename OutputIterator2,
         typename BinaryPredicate,
         typename BinaryFunction >
thrust::pair<OutputIterator1, OutputIterator2>
reduce_by_key(InputIterator1 keys_first,
              InputIterator1 keys_last,
              InputIterator2 values_first,
              OutputIterator1 keys_output,
              OutputIterator2 values_output,
              BinaryPredicate binary_pred,
              BinaryFunction binary_op) {
    typedef typename thrust::iterator_traits<InputIterator1>::value_type  InputKeyType;
    typedef typename thrust::iterator_traits<OutputIterator2>::value_type OutputValueType;

    if (keys_first != keys_last) {
        InputKeyType    temp_key   = *keys_first;
        OutputValueType temp_value = *values_first;

        for (++keys_first, ++values_first;
                keys_first != keys_last;
                ++keys_first, ++values_first) {
            InputKeyType    key   = *keys_first;
            OutputValueType value = *values_first;

            if (binary_pred(temp_key, key)) {
                temp_value = binary_op(temp_value, value);
            } else {
                *keys_output   = temp_key;
                *values_output = temp_value;

                ++keys_output;
                ++values_output;

                temp_key   = key;
                temp_value = value;
            }
        }

        *keys_output   = temp_key;
        *values_output = temp_value;

        ++keys_output;
        ++values_output;
    }

    return thrust::make_pair(keys_output, values_output);
}

} // end namespace host
} // end namespace detail
} // end namespace thrust

